The goals of this research program are to search for better understanding of the functions and mechanisms of ion transport across cell membranes. Investigations range from the complex level of functioning cardiac muscle cells to the basic level of model membrane systems and the physical-chemical properties of membrane molecular systems. The red blood cell remains an important intermediate testing ground for concepts derived from either extreme of this continuum of biological phenomenology. Fundamental investigations are directed toward several major problems in membrane biology: first, the ionic basis of the electrical properties of excitable cells; second, the role of metabolism in maintaining the integrity of the cell membrane, the volume and composition of the cell interior, and the energy needed for active transport processes; third, the role of membrane antigens in modulating membrane function; and fourth, the factors governing the chemical affinities of membrane systems for the transported species. Actual experimental models include cardiac muscle cells grown in tissue culture to controlled and specified geometries, red blood cells from various species with differing metabolisms, ionic composition and membrane properties, various marine plants and animals, and artificial membrane lipid and lipoprotein systems exhibiting useful properties. Observations are collected of electrical properties, including ionic conductances, flux of tracer ion, immunological properties, energy metabolism including turnover of metabolic intermediates and co-factors, ultrastructure of membrane systems, and physical-chemical characteristics of membrane systems, including surface properties, thermal behavior, fluorescence, electron spin resonance, nuclear magnetic resonance, circular dichroism, and absorption spectroscopy.